Paper, film and other web materials used in industry are typically supplied in large rolls wound upon cylindrical cores, usually of cardboard. When the rolls are being wound or unwound in use, the cores are usually mounted on rotatable shafts. Air chunks or air shafts are normally used to lock the core to the rotating shaft so that the rolls rotate with the rotating shaft as a unit. Air chucks are generally short. Air shafts are generally longer, and are used with wider rolls. Both are pressurized by some fluid, usually air, to expand outwardly some gripping element mounted on the air shaft to grip the core of the rolls.
Air shafts usually represent a compromise between weight, which makes the shafts unwieldy to manipulate, and strength, necessary to bear the load of large rolls of material. For example, perforations in the air shaft body through which gripping elements project have a significant negative effect on the strength and rigidity of the air shaft. If the gripping elements are instead mounted on the outside of the shaft, the complexity of the actuating systems for the gripping elements present significant engineering problems.
It is an object of this invention to provide an air shaft that will be strong and effective for gripping a roll core, and yet be light in weight, durable and simple to manufacture and operate.